For a frame with an extreme nasal sweep, what must the dispenser be cautious of?

When dealing with a frame that has an extreme nasal sweep, it is essential for the dispenser to be cautious regarding the patient's pupillary distance (P.D.). Specifically, for patients with a narrow P.D., the extreme nasal sweep can indeed lead to a loss of reading depth.

Reading depth refers to the area of the lens that provides clear vision at reading distances. If the frames are designed in such a way that the optical centers of the lenses do not align well with the patient's eyes, particularly with a narrow P.D., it can negatively impact the visual experience, making it difficult for the patient to see clearly when reading or engaging in tasks that require close vision. The alignment must be precise in order for the lenses to provide the intended optics, and an extreme nasal sweep can interfere with this alignment, particularly if the P.D. is less than ideal for that frame style.

Considering the other options, they involve various aspects of lens fitting or compatibility with progressive addition lenses, which are not as directly impacted by narrow P.D. issues related to extreme nasal sweeps. Thus, the concern around reading depth loss is paramount when selecting frames with significant nasal curvature for patients with certain P.D. measurements.